The linearity requirements for radio transmitters usually require a linearized transmitter because power amplifiers are typically linear only in a limited power range. Power amplifiers are required in radio telecommunication systems to amplify signals before transmitting, because a radio signal attenuates on the radio path. Unfortunately, high-power radio-frequency amplifiers tend to be non-linear devices and therefore in many cases they cause distortion. This distortion is expressed, for example, as Inter-Symbol-Interference or out-off-band power in adjacent frequency bands. Typically in many radio communication systems, there are limitations in specifications for power leakage. Another problem which arises with power amplifiers is that the power adjustment is not accurate enough.
Therefore, it is important to find out the transmitters which do not fulfil the quality requirements by measuring and analysing transmitted signals. A testing method and arrangement suitable for production and in situ testing is especially important.